Process of making paper



Patented May 7, 1940 UNITED STATES PATENT OFFICE PROCESS OF MAKING PAPERHoward D. Meincke, Glencoc, Ill., assignor to A. M. Meincke & Son, Inc,Chicago, 111., a corporation of Illinois 1 Claim.

This invention relates to processes of makin paper; and it includes aprocess of making an improved open textured paper with the fibersthereof cemented together by minute particles of a dried irreversiblestarch gel, which process comprises beating paper pulp with the usualfillers and additions, adding to the pulp in the later stages ofbeating, a fine-grained partly converted starch of a characterreadily-dispersible in cold water and swelling therewith, addingsilicate of soda to the pulp to maintain the pulp at about pH '7 duringthe beating, adding acidic sizing material to the pulp in the laterstages of beating to drop the pH to about 5, and converting the beatenpulp into paper; all as more-fully hereinafter set forth and as claimed.

In making paper, paper pulp is beaten for a long time with water andvarious additions, the beaten pulp then going to the fourdrinier, orwire, to be made into paper. There are operations supplemental to thebeating, in jordans, etc., but in principle the operation is as stated.After formation the web is dried, using heat. Sometimes the .webtemperature becomes rather high. Commercial paper is, of course, basedon cellulose fiber but it contains all sorts of other additions andthere are many types of paper. The use of fillers, inert non-fibrousmaterial, is common and sometimes mineral matter forms a major fractionof the paper. Sizes and cementing bodies are often used. But as a rule,in opentextured paper, there is a fiber-to-fiber union with fibers infrictional engagement.

One of the additions often made to the pulp in the beater is starch,either as raw starch or as cooked starch. Neither material givesentirely satisfactory'results. Raw starch, even in its finely dividedform, is heavy and tends to settle out of water if given opportunity, sothat securing uniform distribution of starch in the heater and in thepaper is not easy. Raw starch is dispersed.

And if complete and uniform dispersion is seon each of the severalfibers. A cemented union of this sort is too stiff; the paper producedis not desirable for most purposes.

The strength shown in various tests of paper varies considerably anddepends on the way the paper is made. Sometimes the strength is due tothe fiber-to-fiber union and sometimes there are agglutinatives orcementing materials in the mixtures, which sheath or coat the fibers andgive a cemented unionbetween fibers. But whatever the fiber union maybe, it is made, so far as possible, uniform all over the sheet; there isno localization of cementing material as far as this can be avoided.Either the paper relies for its strength and its other propertieslargely on a fiber-to-fiber bond or it relies on a cemented.

union between coated fibers. Both types of bond have their advantages.

I have discovered that I can produce a better and stronger paper whichis of a diiierent type; there being spot-wise union of fibersthrough acementing material with fibers elsewhere in the usual fiber-to-fiberengagement. In so doing, I secure two types of bond in the paper,securing the advantages of both so far as strength and other charactersare concerned. The new paper has many of the properties and. advantagesof both pure cellulose papers and starch-sized papers. The appearance ofthe paper does not suffer since the spots of localized cementation aresmall; to the naked eye, and even under a low power magnification, thepaper appears uniform. Its properties as regards taking ink are somewhatbetter than those of a wholly unsized paper and of a completely sizedpaper. There is a moderate and desirable degree of penetration in theuncemented portions of the paper. Spot cementation of fibers, in otherwords, gives two desirable results: a better type of strength and apaper of intermediate properties as regards taking ink.

I have discovered that by the use of specially treated starch I cansecure the desired result of spot-wise cemented engagement between thefibers. Starch on cooking with water swells and is hydrated with theultimate production of a gel. The final gels are irreversible; on dryingand rewetting the gel does not re-appear. But if the starch be cookedwith a limited amount of water for a limited time and the gel comminutedand dried, particles can be secured which in water swell and hydrate,giving a gel particle. There is little tendency for these hydrated gelparticles to coalesce or reunite when stirred up in water. If the gelparticle be again dried, it

becomes irreversible. These properties are utilized in the presentinvention: a granular modified starch of the character described beingplaced in the beater and incorporated with the pulp. It may be added dryor as a pulped suspension. The particles can be readily distributeduniformly through the beater contents in the same sense that mineralparticles can be distributed. When the beater mixture is made into paperon the wire, modified starch particles pass forward and are dried downwith the web giving a cemented engagement between adjacent fiberswherever they occur. The particles persist, so to speak, in the finishedweb. The fibers are, so to speak, spot welded. There is no cooking orfurther gelling as in using raw starch in the web.

In this operation control of the pH is important. For the best resultsthe liquid in the .beater, which may be, largely, returned white water,is kept at a pH of about 7 by additions of silicate of soda. At the endof the beating an acidic sizing material such as alum, is added to thepulp to drop the pH to about 5. At a-pH of '7 the modified starchparticles have little stickiness; they do not tend to clump andcoagulate in the water, while at a pH of 5 in making the web, stickinessdoes develop. In other words, modified starch particles are keptnon-sticky during incorporation in the beater charge and are allowed todevelop stickiness, or adhesive power, afterwards.

There are various conmiercial starch preparations, some made for foodpurposes, which are useful in the described invention. However, a goodpreparation may be made by heating starch under pressure with four orfive times its volume of water until there is complete interactionbetween the starch and the water and then delivering the hot material ona heated drying roll. After drying it is removed from the roll andmechanically comminuted. Better results are obtained by feeding thestarch between a pair of heated rollers. The comminution should be to amoderately fine powder; fine enough so that in the paper it is not quitevisible to the naked eye. In this operation the original starch granulesdisappear and the new particles bear no necessary relation to theoriginal starch granules. A preparation of this sort resembles ordinarytapioca except for the size of the grains. In fact, a preparation usefulfor the present purposes can be made by fine grinding commercialtapioca.

In carrying out my process, I mix a suitable quantity of convertedstarch w'ith the pulp in the beater. The starch may be added either indry granular form or in water suspension, and in a typical case is addedin a proportionof about 6o 1 to 2 per cent by weight on'the (dry) pulp.

The pulp in the beater is kept at a pH of about 7, that is, about atneutrality, during the addition of the starch and the following beating.Since it is common practice to return back-water from the save-ails tothe beater, (white water) and as this water is acid, to maintain theproper pH it is usually necessary to add an alkaline agent to the pulp.Silicate of soda is best.

When beating is finished or nearly so, I drop the pH of the pulp toabout 5. This is conveniently done by adding alum or other sizingmaterial to the pulp.

The beaten pulp is then refined in Jordan engines in the usual way andis made into paper.

As a result of this process there is obtained a paper which hasdistributed isolated spots where the fibers are bonded by the dry gelwith other areas where the ordinary fiber-.to-fiber union exists. If thestarch product be ground to the proper fineness, a paper. is secured ofuniform appearance to the naked eye, but under a low power lens showingspots of cemented fiber and areas of uncemented fiber. On bluing thepaper with iodine it presents a uniformly blue appearance, but under thelens shows deep blue spots of cemented union and paler areas whereuncemented fibers occur. If coarser starch product is used, the spots ofstarch bonded fibers may become large enough to be visible and give thepaper an uneven or mottled look.-

Paper with localized spot union as described is considerably stronger byall the usual tests, bending, tension, fold, etc., than ordinary papersincluding starch-sized papers, while it has much of the open-texturedand other desirable characteristics of ordinary paper. Moreover the newpaper is less subject to changes due to variations in humidity andtemperature. It is quite possible to size, coat and otherwise treat thenew paper in ways in which prior paper is treated, there being asufficient total area where the texture is open, and the union of theordinary type, to permit this.

What I claim is:

The process of making an open-textured high strength paper whichcomprises beating paper pulp in a beater for a prolonged period; addingto and beating into the contents of the beater a readily dispersiblefine-grained starch product produced by heating starch under pressurewith 4 to 5 times its volume of water until interaction between starchand water is complete and heating the suspension to dryness in thinlayers and comminuting the dried product to subvisible powder particles;maintaining the pH oi. the' starch-pulp mixture in the beater at aboutpH '7 by addition of sodium silicate; adding alum to the beater mixtureto reduce the pH to about 5 and converting the mixture into paper.

HOWARD D. MEINCKE.

